Real Time Analysis and Display of Scanning Lidar Scattering Data

We describe software for an IBM compatible personal computer (PC) that we have developed and used to collect and analyze backscatter data from a multi-wavelength Mie-Rayleigh scanning lidar system. Both one and two-dimensional distributions of optical scattering coefficients are calculated from the lidar return signals and displayed in real time. Although we are using the software for analyzing marine aerosols, the modular nature of the software and data acquisition drivers make it straightforward to adapt the software to different systems, such as differential absorption lidar (DIAL) and oceanic lidars. We show examples of both horizontal and vertical Mie-Rayleigh lidar scans collected at the Makai Pier and Bellows Beach on the northeast side of the island of Oahu.     

Determination of stratospheric aerosol parameters from two-wavelength lidar sensing data

We calculate the microphysical characteristics of stratospheric aerosol from lidar-sensing data at wavelengths of 355 and 532 nm using a priori information about the aerosol spectra obtained from balloon and aircraft measurement data. We analyze the mode structure of the spectra and its coupling with the integral microphysical characteristics of aerosol. For most implementations, it was shown that two aerosol modes (of background and volcanic natures) make commensurate contributions to integral aerosol characteristics, which makes it difficult to use the traditional method of model estimates. It is more efficient to use an optical model of a statistical character that is based on approximation dependences between the required integral aerosol characteristics and lidar-measured optical characteristics. We found that the area, volume, and effective size of particles and the lidar ratio at a wavelength of 355 nm correlated with the absolute values of backscattering coefficients at wavelengths of 355 or 532 nm and the lidar ratio at the wavelength of 532 nm correlated with the ratio of backscattering coefficients at these wavelengths. We estimate the error in the determination of integral characteristics of aerosol using the model developed. The model efficiency is demonstrated on real data of stratospheric aerosol lidar sensing.     

浅海双跃层脉冲声传播

利用在东海测量的双跃层声速剖面和修改的单跃层声速剖面,数值模拟了2种跃层条件下不同收发深度声脉冲传播的波形。模拟结果表明,当声源或接收器位于上混合层时,信号波形在2种条件下都出现梳状多途结构。当声源和接收器都位于下混合层时,信号波形在2种条件下均相似。当声源位于中间均匀层时,信号波形在除上混合层以外的4层都有显著差异。用简正波的深度-简正波号域的幅度和相应的群速度解释了双跃层和单跃层声速剖面条件下信号波形特点以及异同的原因。     

Methods to Improve the Long Distance Time-Varying Channel Transmission Performance of Expendable Profiler

To improve the transmission performance of XCTD channel, this paper proposes a method to measure directly and fit the channel transmission characteristics by using frequency sweeping method. Sinusoidal signals with a frequency range of 100 Hz to 10 k Hz and an interval of 100 Hz are used to measure transmission characteristics of channels with lengths of 300 m, 800 m, 1300 m, and 1800 m. The correctness of the fitted channel characteristics by transmitting square wave, composite waves of different frequencies, and ASK modulation are verified. The results show that when the frequency of the signal is below 1500 Hz, the channel has very little effect on the signal. The signal compensated for amplitude and phase at the receiver is not as good as the uncompensated signal.Alternatively, when the signal frequency is above 1500 Hz, the channel distorts the signal. The quality of signal compensated for amplitude and phase at receiver is better than that of the uncompensated signal. Thus, we can select the appropriate frequency for XCTD system and the appropriate way to process the received signals. Signals below1500 Hz can be directly used at the receiving end. Signals above 1500 Hz are used after amplitude and phase compensation at the receiving end.     

Advancements in the U.S. army corps of engineers hydrographic survey capabilities: The SHOALS system

In an effort to modernize its hydrographic survey capabilities, the U.S. Army Corps of Engineers has undertaken a joint development program with Canada to construct and field test an operational prototype airborne lidar bathymeter system. The construction and field verification effort of this program began March 1990 with field tests scheduled for winter 1993. The system will be built by Optech, Inc., based on their design of the LARSEN 500, the only commercial lidar system currently producing bathymetric surveys.

The Scanning Hydrographic Operational Airborne Lidar Survey (SHOALS) system will operate out of a medium‐sized helicopter such as the Bell 212 at approximately 200 meters altitude where the laser scanning system generates a swath width of just over 140 meters. System requirements dictate a laser operating at 200 Hz in both the blue‐green wave length for maximum water depth penetration and the infrared for surface interface recognition. Each laser shot strikes the water surface at a known location where its energy is partially reflected back to the receiver and partially transmitted through the water column. Transmitted energy undergoes scattering and absorption along its path to the bottom where the remaining energy is then reflected back to the receiver.

The Transceiver, Positioning, Acquisition, Control and Display, and Ground Based Data Processing subsystems make up the SHOALS system. These subsystems have been designed, constructed, and currently are being laboratory tested prior to total system integration and field testing. This article presents the system's design and discusses system use following development.     

Combining Lidar Elevation Data and IKONOS Multispectral Imagery for Coastal Classification Mapping

This article studies the effect of airborne lidar (surface) elevation data on the classification of multispectral IKONOS images over a coastal area. The lidar data and IKONOS images are treated as independent multiple bands to conduct the classification. To do so, the lidar elevation data is first resampled to the same ground spacing interval and stretched to the same radiometric range as the IKONOS images. An unsupervised classification based on the ISODATA algorithm is then used to determine a class schema of six classes: road, water, marsh, roof, tree, and sand. Training sites and checking sites are selected over the lidar-IKONOS merged data set for the subsequent supervised classification and quality evaluation. The complete confusion matrices and average quality indices are presented to assess and compare the classification results. It is shown that the inclusion of the lidar elevation data benefits the separation of classes that have similar spectral characteristics, such as roof and road, water and marsh. The overall classification errors, especially the false positive errors, are reduced by up to 50%. Moreover, by using the lidar elevation data, the classification results show more realistic and homogeneous distribution of geographic features. This property will benefit the subsequent vectorization of the classification maps and the integration of the vector data into a geographical information system.     

Combining Lidar Elevation Data and IKONOS Multispectral Imagery for Coastal Classification Mapping

This article studies the effect of airborne lidar (surface) elevation data on the classification of multispectral IKONOS images over a coastal area. The lidar data and IKONOS images are treated as independent multiple bands to conduct the classification. To do so, the lidar elevation data is first resampled to the same ground spacing interval and stretched to the same radiometric range as the IKONOS images. An unsupervised classification based on the ISODATA algorithm is then used to determine a class schema of six classes: road, water, marsh, roof, tree, and sand. Training sites and checking sites are selected over the lidar-IKONOS merged data set for the subsequent supervised classification and quality evaluation. The complete confusion matrices and average quality indices are presented to assess and compare the classification results. It is shown that the inclusion of the lidar elevation data benefits the separation of classes that have similar spectral characteristics, such as roof and road, water and marsh. The overall classification errors, especially the false positive errors, are reduced by up to 50%. Moreover, by using the lidar elevation data, the classification results show more realistic and homogeneous distribution of geographic features. This property will benefit the subsequent vectorization of the classification maps and the integration of the vector data into a geographical information system.     

Retrieval of integral parameters of tropospheric aerosol from two-wavelength lidar sounding

A scheme of interpreting the data of two-wavelength lidar sounding is proposed. The scheme is based on functional relationships between the lidar ratios and between some integral characteristics of aerosol and the ratio of the backscattering coefficients at the sounding wavelengths. The AERONET data, results of contact aerosol measurements and multiwavelength lidar sounding, and the OPAC aerosol model are used to find these functional relationships, which are statistical in character. Analysis of data is made separately for continental, dust, oceanic, and smoke aerosols. Backscattering for mineral aerosol fractions are calculated for a model of randomly oriented spheroids. A numerical experiment shows that the errors in determining a number of integral parameters of aerosol (extinction coefficient, characteristic radius of particles, volume concentrations) that are due to the statistical straggling of lidar ratios and other specified integral characteristics are no greater than 32% if the optical thickness of the sounding layer is no greater than 1.     

Spatial modulation experiments in the underwater acoustic channel

A modulation technique for increasing the reliable data rate achievable by an underwater acoustic communication system is presented and demonstrated. The technique, termed spatial modulation, seeks to control the spatial distribution of signal energy such that the single physical ocean channel supports multiple parallel communication channels. Given a signal energy constraint, a communication architecture with access to parallel channels will have increased capacity and reliability as compared to one with access to a single channel. Results from two experiments demonstrate higher obtainable data rates and power throughput for a system employing spatial modulation than for one that does not. The demonstrated benefits were characterized by an equivalent SNR gain of over 5 dB in the first experiment. In the second experiment, using two element source and receiver arrays with apertures of 0.9 m, a coherently modulated signal was shown to offer nearly 50% greater capacity by using spatial modulation than by using temporal modulation alone.     

MULTIPATH STRUCTURES OF SIGNAL WAVEFORMS IN SHALLOW WATER WITH THERMOCLINE

It has been observed experimentally that the signal waveforms in shallow water with thermocline have regular multipath structures and the waveforms of received signals are strongly dependent on the depths of the source and the receiver. When both the source and the receiver are located above the thermocline, each sigrtal received consists of a train of almost equispaced wave-packets. The time interval iswhere H, d, C0 and C1 are parameters of the sound velocity profile. When the source is below the thermocline and the receiver is above, the time intervals between wave-packets are τ and (T- τ)where η is the distance from the source to the bottom.These observed regularities of waveforms may be used for monitoring the fluctuation of the thermocline in shallow water.     

袭港热带气旋持续时间长期频率分析

香港经常受到西北太平洋热带气旋的影响,对该地区热带气旋持续时间的研究有助于经济社会的稳定发展。按照气象和天文台警告信号,热带气旋分为不同的强度等级。建立热带气旋持续时间的Poisson-Weibull复合分布模型,相应获得持续时间重现值的求解公式,分别用于不同热带气旋分类下持续时间多年一遇重现值的计算中。基于1987-2016年袭港热带气旋数据的分析结果表明,Poisson-Weibull分布适用于不同的持续时间分类样本;强的热带气旋经常会伴随较长的持续时间,这将会对该地区造成更为严重的破坏,这可为防灾减灾提供参考。     

On Optimal Frequencies of Acoustic in-situ Detector for Seafloor Hydrothermal Vents

The approach to determine working frequencies of acoustic in-situ detector for seafloor hydrothermal fluid is presented. Based on the research of deep-sea noise and the sound generated by mid-ocean ridge black smoker hydrothermal vents, and on the hydrothermal-vent animal hearing ranges, coupled with influences of suspended particles of hydrothermal on acoustic attenuation under different frequencies, the optimal frequency range for detection of acoustical signal near black smokers is determined. The optimal frequencies providing the maximum ratio of receiver signal to background noise are obtained. We have developed a laboratory experimental setup for the optimal frequencies selection. In particular, we evaluated time-of-flight performance with respect to the source signal parameters of center frequency and bandwidth. The experimental results confirm the effectiveness of our approach. Current results indicate that individual transducers operated in the range of 18 ～ 25 kHz are immune to most interfering sounds and suitable for our system.     

负跃层浅海中信号波形的多速结构

海洋中水声信号波形的变化规律是一个重要的研究课题,利用信号波形特征可能识别不同的水下目标、提高信号处理的增益.信号波形的规律性也可用来监测某些海洋环境参数的变化.深海中存在较稳定的水下声道,文研究过水下声道中信号波形规律.由于浅海环境的复杂性,海水介质及其边界在空间与时间上存在着有规则的与随机的变化.因而浅海中脉冲信号的波形结构需要进行专门的研究.本文仅就负跃层浅海中的信号波形规律进行一些探讨.     

一种新型多功能海洋浮标

介绍一种多功能海洋考察与观测用浮标的结构、性能。浮标带有短波无线电遥控和数据传输功能、可外挂多种传感器;该浮标采用小水线结构,在较高海况下,具有较好的安定性。浮标配置了差分型全球定位（DGPS）接收机和短波电台,可对浮标的位置和工作状况实施实时监测,对浮标的工作程式实时遥控并进行必要的数据传输。浮标电子舱内具有大容量多通道数据采集记录系统,DGPS的lpps（1 pulse per second）信号被用于多浮标数据采集的精确同步。浮标可用于海洋监测、考察;也可用于水下目标高精度大地坐标测量等海洋工程。     

机载海洋激光荧光雷达测量海表层叶绿素a浓度的算法研究

基于中国海洋大学研制的我国首台机载海洋激光荧光雷达系统及其测量海水中叶绿素a浓度的方法;对该系统在烟台至荣成沿岸海域进行实验的情况作一回顾,并对实验数据进行了处理,采用拉曼校正归一方法,反演了海表层的叶绿素a浓度,同时利用激光雷达方程反演出了海水的衰减系数;另外,提出了最小二乘拟合提取信号峰值的新反演算法。反演结果与往年同时期采集数据较为吻合,使用最小二乘拟合提取信号峰值的算法反演的叶绿素a浓度更接近于近期实地测得的结果。     

Model of lidar images of nonlinear internal waves

An analytical model of a lidar image of a nonlinear internal wave (IW) described by the Kortewegde Vries equation (KdV) is developed. Peculiarities of lidar images of the nonlinear IW are processed and analyzed using real profiles of hydrooptical and hydrological characteristics in the Barents Sea. Regularities of variations in the thickness of turbid layers caused by the nonlinear IW are found.     

Effect that jet streams have on the vertical ozone distribution and characteristics of tropopause inversion layer in the far east region

The paper describes a lidar and presents the results of lidar sensing of the vertical ozone distribution (VOD); the lidar measurements are analyzed together with data from a network of meteorological stations situated along the 132° E meridian. VODs over Primorye and Japan in the winter period are compared. An analysis showed that an interrelation exists between the subtropical jet stream and the structures of VOD and tropopause inversion layer. Specifically, the region of the VOD local maximum above the tropopause is in the upper part of the tropopause inversion layer and the width of the maximum depends on the distance from the core of the subtropical jet stream. It is found that the local ozone minimum in the lower stratosphere corresponds to the local minimum of the squared Brunt-Vaisala frequency within this same altitude range in the winter season, when two tropopauses frequently overlap. It is conjectured that the local ozone maximum and tropopause inversion layer may be associated with mixing processes in the layer where stratospheric and tropospheric circulation cells come into contact near the core of the subtropical jet stream.     

Signal processing for precise ocean mapping

In this work a bottom return signal model and accompanying signal processor are described for a wide swath bottom mapping system. An incoherent scattering model is employed under the assumptions that the bottom is a random rough surface composed of a large number of independent scatters with spatial correlation distance negligible relative to the ensonified area. The envelope of the signal received from the various spatial directions is modeled as a smooth, nearly Gaussian-shaped function representing the effects of the twoway spatial beam pattern, angle of incidence, and depth corrupted by multiplicative and additive noise stochastic processes. A signal processor is derived which makes use of the a priori information vested in this smooth function to provide a matched filter for the received signal envelope for each spatial direction. Computer simulation results are presented and the performance of the signal processor examined in a qualitative fashion.     

Wave height statistical characteristic analysis

When exploring the temporal and spatial change law of ocean environment, the most common method used is using smaller-scale observed data to derive the change law for a larger-scale system. For instance, using 30-year observation data to derive 100-year return period design wave height. Therefore, the study of inherent self-similarity in ocean hydrological elements becomes increasingly important to the study of multi-year return period design wave height derivation. In this paper, we introduced multifractal to analyze the statistical characteristics of wave height series data observed from oceanic hydrological station. An improvement is made to address the existing problems of the multifractal detrended fluctuation analysis (MF-DFA) method, where trend function showed a discontinuity between intervals. The improved MFDFA method is based on signal mode decomposition, replacing piecewise polynomial fitting used in the original method. We applied the proposed method to the wave height data collected at Chaolian Island, Shandong, China, from 1963 to 1989 and was able to conclude the wave height sequence presented weak multi-fractality. This result provided strong support to the past research on the derivation of multi-year return period design wave height with observed data. Moreover, the new method proposed in this paper also provides a new perspective to explore the intrinsic characteristic of data.     

Lidar sounding of the optical parameter of atmospheric turbulence

The operation of a lidar intended for clear air turbulence (CAT) positioning on the basis of the backscatter enhancement (BSE) effect is analyzed using a turbulence model with a power-law spectrum. Systematic distortions occurring due to a need to regularize the lidar positioning problem solution are estimated. It is shown that the effect of molecular viscosity of air on the positioning result can be neglected if the wave parameter, which characterizes the diffraction manifestation, is higher than 3. This corresponds to sounding ranges of more than 1 km for optical or UV lidars. The analysis results show that the BSE lidar positioning accuracy weakly depends on the exponent in the turbulence spectrum in regions of severe turbulence. The results can justify a physical experiment for the design of an aircraft system for the lidar detection of CAT regions ahead of the flight course.